Shoulder replacement is a surgical procedure in which all or part of the glenohumeral joint is replaced by a prosthetic implant. Such joint replacement surgery generally is conducted to relieve arthritis pain or fix severe physical joint damage.
Shoulder replacement surgery is an option for treatment of severe arthritis of the shoulder joint. Arthritis is a condition that affects the cartilage of the joints. As the cartilage lining wears away, the protective lining between the bones is lost. When this happens, painful bone-on-bone arthritis develops. Severe shoulder arthritis is quite painful, and it can cause restriction of motion. While this may be tolerated with some medications and lifestyle adjustments, there may come a time when surgical treatment is necessary.
There are a few major approaches to access the shoulder joint. The first is the deltopectoral approach, which saves the deltoid, but requires the subscapularis to be cut. The second is the trans deltoid approach, which provides a straight on approach at the glenoid. However, during this approach the deltoid is put at risk for potential damage.
Shoulder replacement, also known as shoulder arthroplasty or glenohumeral arthroplasty, was pioneered by the French surgeon Jules Emile Pean in 1893. His procedure consisted of physically smoothing the shoulder joint and implanting platinum and rubber materials. The next notable case in the evolution of shoulder replacement procedures was in 1955 when Charles Neer conducted the first hemiarthroplasty, essentially replacing only the humeral head, leaving the natural shoulder socket, or glenoid, intact. This procedure grew exponentially in popularity as time progressed; however, patients often developed cartilage loss on their glenoid surface as well, leading to pain and glenoid erosion. This prompted the development of a procedure to replace not only the humeral component, but the glenoid component as well.
Throughout the development of the procedures, it became well accepted that the rotator cuff muscles were essential to producing the best outcomes in terms of strength, range of motion, and a decrease in pain. In addition to this finding, physical constraints of the normal ball-and-socket anatomy of the shoulder limited most developments in one way or another. For example, a heavily constrained system limited range of motion and the inherent anatomy of the glenoid proved difficult to cement prosthetics and fixate components without fracturing it. These challenges and high rates of failure led to the development of the reverse total shoulder arthroplasty to overcome the limitations imposed by the natural shoulder anatomy.
The 1970s saw an exponential increase in surgical approaches using this methodology, and the number and variation of surgical techniques are many. However, in 1985 Paul Grammont emerged with a superior technique that is the basis for most reverse shoulder replacement procedures today.
In traditional total shoulder arthroplasty, the approach begins with separating the deltoid muscle from the pectoral muscles, facilitating access to the shoulder (glenohumeral) joint through a relatively nerve free passageway. The shoulder joint is initially covered by the rotator cuff muscles (subscapularis, supraspinatus, infraspinatus & teres minor) and the joint capsule (glenohumeral ligaments). Typically, a single rotator cuff muscle is identified and cut to allow direct access to the shoulder joint. As this point, the surgeon can remove the arthritic portions of the joint and then secure the ball and socket prostheses within the joint.
The development of safer, more effective techniques has led to increased use of reverse total shoulder arthroplasty. Reverse total shoulder arthroplasties are typically indicated when the rotator cuff muscles are severely damaged.
Many existing reverse shoulder systems require a baseplate and a glenosphere. These systems generally differ from one another in how the baseplate is fastened to the glenoid cavity and how the glenosphere becomes engaged to the baseplate. In some systems, the baseplate may be fastened to the glenoid cavity of the scapula by a plurality of screws and a glenosphere having a convex joint surface may be screwed into the baseplate using an axial threaded feature and/or taper that is a part of the baseplate. In other systems, the glenosphere may engage the baseplate solely via a taper connection.
In cases where the glenosphere becomes engaged to the baseplate through either a threaded or taper connection, the glenosphere and baseplate may become separated after a certain length of time. This may cause the glenosphere to tilt with respect to the baseplate or in some cases even separate therefrom. In either situation, the baseplate and glenosphere become misaligned.
Some systems include first fastening a central screw to a glenosphere and then guiding the connection between the baseplate and glenosphere via the central screw. Guiding the connection between the baseplate and glenosphere is generally an important consideration due to minimal access and visibility that the surgeon may have during a reverse shoulder procedure. Access to the baseplate is generally narrow making it relatively difficult for the surgeon to have the visibility needed to correctly align the engagement between a baseplate and glenosphere.
What is needed in the art is a shoulder implant that improves upon prior art devices by providing design advantages that result in less bone loss, improved bone graft retention, and greater initial and long-term implant fixation.